Large mechanical assemblies must often be maintained by several threaded rods or studs. A Multiple Stud Tensioning Machine (from now on mentioned by its acronym MSTM) is then used to position, screw and unscrew as well as pre-tension a plurality of threaded studs. Examples are the attachment of parts of wind turbines or of the protecting cover of nuclear power reactor shells. A number of threaded studs are usually arranged in a circular row for attachment of such kind of large mechanical assemblies.
In order to facilitate the attachment operations, for example of the protecting cover to a nuclear reactor shell of a power station, a supporting ring assembly is provided, said assembly being moved from above on the cylindrical cover installed on the nuclear power shell. The complete set of attachment studs is supported by the supporting ring which is also provided with all necessary components for screwing and unscrewing the studs as well as tensioning them in a longitudinal direction before tightening the corresponding reaction nuts. In order to fulfill those tasks, the supporting ring is usually equipped with at least one and preferably two robot units capable of being moved along the periphery of the supporting ring for screwing or unscrewing the working studs and the reaction nuts two by two within the nuclear power shell. The longitudinal traction force for pre-stressing each individual stud before tightening is produced by a plurality of hydraulic stud tensioners, each of which is mounted on the head of a respective stud. Such a multiple stud tensioning machine is known from WO 2011/120589A1.
Since such a MSTM is sometimes used once a year or even less, and for only a few hours, it is key to ensure a proper functioning of the machine before it is used to screw or unscrew the studs.
Further, some maintenance operations of the power station require the inspection and cleaning of the working studs, during an outage operation. Given that the weight of a stud can sometimes reach a few hundred kilograms, the sole manipulation of the studs before and during their inspection and cleaning today takes time and requires the usage of additional mechanical parts.
Consequently, there is room for improvement.